Correctly set auto-growing array's element

Prior to this commit, the implementation of processKeyedProperty() in
AbstractNestablePropertyAccessor resulted in a
`java.lang.IllegalArgumentException: array element type mismatch` when
the property expression had more than one property key and the last key
should cause the array to grow automatically.

For example, given a property `int[][] multiArray` and property
expression `multiArray[1][3]`, the `processKeyedProperty()` method
created a new array object and assigned it to `multiArray`; whereas,
the new array object should have be assigned to `multiArray[1]`.

This commit fixes this issue.

Closes gh-26600

spring-beans/src/test/java/org/springframework/beans/BeanWrapperAutoGrowingTests.java

@@ -99,6 +99,12 @@ public class BeanWrapperAutoGrowingTests {
 		assertThat(bean.getMultiArray()[0][0]).isInstanceOf(Bean.class);
 	}
 
+	@Test
+	public void setPropertyValueAutoGrowMultiDimensionalArray() {
+		wrapper.setPropertyValue("multiArray[2][3]", new Bean());
+		assertThat(bean.getMultiArray()[2][3]).isInstanceOf(Bean.class);
+	}
+
 	@Test
 	public void getPropertyValueAutoGrowList() {
 		assertNotNull(wrapper.getPropertyValue("list[0]"));